Drawn brazed strand (DBS) is a type of cable characterized by good strength, stress resistance and conductivity properties that is frequently used in applications where cable failure is highly undesirable. One example is in the field of implantable medical devices, such as pacemakers, where the repair or replacement of electrical cables in the leads would require invasive surgery.
DBS typically includes a conductive element encased in a protective sheath. The conductive element is formed of a number of conductive strands twisted together. Each strand is formed from a plurality of individual alloy wires woven or wrapped about a core wire. The core wire is generally soft but highly conductive, and is usually made of silver, while the alloy wires are less conductive but stronger. The sheath is typically formed of a non-conductive material such as silicone or polyurethane. The sheath increases cable strength and also provides a protective electrical and environmental barrier around the conductive element.
Once the wires are formed into strands and the strands are twisted into the cable, the conductive element is inserted, or stringed, through one end of the sheath. Prior to assembling the conductive element with the sheath, a lubricant such as alcohol is injected into the sheath. The alcohol chemically interacts with the interior silicone wall of the tubing to provide a more lubricious surface. The conductive element is then pushed into and through the tube from one end.
This process has many drawbacks. First, despite lubricating the interior of the sheath, the conductive element has a tendency to become kinked within the sheath. Kinking degrades the conductive properties and strength of the cable such that kinked units are usually discarded. Second, alcohol is highly combustible and emits noxious fumes and odors bothersome to operators. Sometimes it is necessary to provide a venting system to maintain adequate air quality and additional fire control precautions must be employed. Third, residual alcohol must be removed from the stringed cable before further processing can be carried out. This is typically accomplished by placing the stringed cable into a furnace or near some other source of heat to evaporate the alcohol. Finally, the alcohol supply may become contaminated. Contamination can affect the lubricity between the conductive element and the sheath, and may cause particulates to be deposited within the sheath after the alcohol is evaporated.
Therefore, there exists a need for an improved method of stringing cables such as DBS type cable. There is a further need for a method that does not require the use of alcohol.